Microbiological testing for microbial growth and metabolism often takes on many forms, including biological indicator (BI) testing (e.g., sterility testing), biological oxygen demand (BOD) testing, and antibiotic drug resistance/sensitivity testing of infections. Although processes exist for all three kinds of microbial testing, such processes usually involve long incubation times for whatever microorganisms are present in a particular sample to grow out enough to be noticed by visual detection systems. Thus, the answer to each question, regarding the degree of contamination for BOD testing, or if sterilization has effectively eliminated viable microorganisms in BI testing, or if a particular strain of infectious microorganism will be killed by a particular drug, each take long time periods of up to about 48 hours to provide test results. There is a tremendous need in the art to conduct such tests and obtain results much faster. The present invention is designed to provide inventive tests, integrated sensor materials, testing apparatus, and methods designed to increase the speed of such tests by utilizing oxygen sensing measurements in a controlled microenvironment.
Medical procedures worldwide often require sterile environments, equipment, apparatus and devices to prevent patient infection. While disposable or “single use” equipment can be packaged and used under sterile conditions, reusable equipment, apparatus and devices (e.g., surgical tools) require thorough washing and sterilization prior to each use. The assurance of an adequate sterilization cycle is critical in the prevention of infection and the spread of diseases. Furthermore, before using instrumentation in surgical and dental procedures, personnel need to know if the instruments have been properly sterilized, as close to completion of the sterilization as possible. Unfortunately, conventional tests for sterility assurance require a lengthy time and subjective observations before the sufficiency of the process can be evaluated.
A biological indicator (BI) testing device can be included in a sterilization run, but typically the sensing element consists of bacteria that must be grown in culture media at an elevated temperature for a period of days before the adequacy of the sterilization can be determined. The viability of any bacteria remaining after the sterilization is determined by measuring bacterial growth or metabolic byproducts. If there is no growth, then the sterilization cycle was effective and the bacteria adequately destroyed. If growth occurs, then the sterilization cycle was faulty or incomplete. There is a need in the art to find this answer as quickly and reliably as possible.
Most of the conventional growth tests are conducted at test facilities outside the medical or dental offices, which can add to delay and cost in obtaining the results. Further, extraneous bacteria may be inadvertently introduced into the test during handling, thereby increasing the chances for incorrect results. Often, the instruments contained within a particular sterilization cycle cannot be quarantined and must be used at risk before the results of a particular growth test are known. Therefore, it is desirable to determine the results of a sterilization cycle within a short period of time, such that the sterility of the instruments sterilized is known before their use on a patient.
BI tests have been developed which reduce the handling requirements and thereby decrease the risk for inadvertent contamination. Other improvements include the use of a pH dye in the growth media which changes color to indicate spore growth. Thus, “self-contained BI's” which permit a biological sample to be exposed to a sterilizing environment (along with the desired articles to be sterilized) with the unit subsequently providing a means of sealing and immersing the biological sample in a growth-inducing medium upon activation of the unit are one example. The inclusion of indicator dyes in the growth medium help provide a more easily observable measure of bacterial growth than simple turbidity changes. These improvements still require long incubation periods, frequent observation of the BI and significant user training to differentiate the color change to expect upon growth.
There are commercially-available chemical indicators which indicate sterility by a color change or a change from a liquid or solid state. Although the results are known immediately after the sterilization cycle, the results are based upon the fact that a particular temperature has been reached or that ethylene oxide gas was present during the sterilization cycle. So called “sterilization integrators” are similarly limited to measuring only a few sterilization parameters. Even the fluorescent enzyme inactivation tests recently introduced do not adequately reflect the complexity of the sterilization process. In the art and by statute, it is generally recognized that only tests utilizing intact, live organisms adequately integrate the chemical and physical parameters necessary to affect sterilization.
Accepted methods for sterility assurance testing involve biological indicator (BI) tests based upon killing a well characterized, defined population of organisms during the sterilization process. Detection of organism growth, i.e. sterilization failure, is often visual wherein a test sample containing viable microorganisms is placed into the sterilizer and after completion of sterilization, the test sample is incubated with growth media for up to 7 days and “read” for evidence of microorganism growth indicated by changes in turbidity or subtle color changes in the media. More commonly now, a colorimetric pH indicator is added such as phenol red or bromthymol-blue to help in detecting a metabolic process occurring.
The shortcoming of these BI tests is reflected in the long times required to make the determination of metabolic activity. Visualizing turbidity requires relatively long optical path lengths to achieve sufficient opacity for viewing, necessitating large media volumes, and are highly subjective during the early grow out period. Optical detection of pH changes with pH indicators similarly requires relatively long path lengths and additionally must overcome the high pH buffering of biological media. These constraints on conventional BI tests lead to long times to confirmation of test results and necessitates that most equipment be used at risk.
Therefore, there is a need in the art to improve upon BI test methodologies to provide more sensitive testing procedures and devices and to provide for earlier readouts of the test results. The present invention addresses these needs in the art.
When patients have an infection, often times the infectious agent is found within blood or other tissue samples. Such bacterial infections are serious and life-threatening and require effective treatment as soon as possible. Current procedures involve culturing blood or tissue samples to identify the presence of the organisms. Further identification of the isolated organism requires biochemical tests and antimicrobial sensitivity/resistance tests to determine effective treatments. In one method, the isolated organism is plated in a confluent layer on appropriate agar plates with small paper disks, each containing a different antibiotic. This culture test looks for area of clear media (absence of bacterial organism) in an otherwise cloudy lawn of bacterial growth to find that drug or those drugs likely to be effective in combating the infection. Unfortunately, the culture test for resistance/sensitivity takes up to 24 hours to perform and patients require treatment to be initiated much sooner. Therefore, the medical practitioner will prescribe broad spectrum antimicrobial to treat likely cause of the bacturemia. Microbial insensitivity to the antibiotic agent will require reevaluation of treatment options, patient retrieval and further monitoring for clinical progress. The present invention was made to apply oxygen sensing technology developed in a microenvironment in BI testing to drug resistance/sensitivity testing of many potential therapeutic agents.